The present application relates generally to the protection of plants from plant pathogens and in particular from fungal pathogens. The present methods especially provide a multivalent approach to inhibiting pathogen infection in plants and to ameliorate damage to susceptible plants.
Bibliographic details of the publications referred to by author in this specification are collected alphabetically at the end of the description.
Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.
Crop losses due to infection by plant pathogens such as fungal pathogens are a major problem in the agricultural industry and each year, millions of dollars are spent on the application of fungicides to curb these losses (Oerke and Dehne, 2004). There is a need to identify new anti-microbial agents and strategies for dealing with infection by pathogens such as fungi. This is particularly important given the propensity for pathogens to develop resistance.
Antimicrobial peptides have evolved to protect organisms from pathogens. Their specificity is largely dependent on the organism from which they originate, probably due to evolutionary pressure placed on these organisms by various pathogens. As such, peptides isolated from mammalian species generally exhibit a higher degree of activity toward bacterial pathogens compared to fungal pathogens, presumably due to the higher risk of infection from bacteria. In contrast, plant antimicrobial peptides generally display higher antifungal activity due to the higher risk of fungal infection faced by plants.
Plant defensins represent one class of antimicrobial peptides (reviewed by Lay and Anderson, 2005). There is a wide variety of defensins with differing spatial and temporal patterns of expression and spectra of activity.
The mechanisms underlying the specificity of these peptides remain unknown, although interactions with plasma membrane components are presumed to be involved. Since membrane permeabilization is a common activity of many antimicrobial peptides and the membrane composition of various cell types is highly variable, the presence of specific lipids is postulated in some cases to be responsible for the efficacy of antimicrobial peptides. In particular, the plasma membrane of bacterial cells contains negatively charged phospholipids in the outer layer while mammalian cells do not (Matsuzaki, 1999). These negatively charged lipids could interact with positively charged antimicrobial peptides. In support of this hypothesis, in vitro studies have demonstrated that the presence of negatively charged lipids is important for the membrane permeabilizing activity of a number of antimicrobial peptides (Matsuzaki et al, 1995; Matsuzaki, 1999; Epand et al, 2006).
Membrane permeabilization has been suggested as a mechanism of action for some plant defensins, although the mechanism of permeabilization has not been investigated. In the case of the plant defensins RsAFP2 and DmAMP1, permeabilization is proposed to involve a specific receptor on the cell surface. The presence of specific sphingolipids in the plasma membrane is also required for the activity of these defensins, possibly as binding sites (Thevissen et al, 2000; Thevissen et al, 2004; Thevissen et al, 2005; Ramamoorthy et al, 2007).
Plant pathogens induce significant plant yield loss and current strategies for pathogen control are both expensive and potentially damaging to the environment. Given the need to improve the economy of agriculture production, new strategies are required for protecting agronomic and ornamentally important plants from a range of diseases, especially fungal disease.